U.S. patent number 7,820,990 [Application Number 12/000,298] was granted by the patent office on 2010-10-26 for system, method and apparatus for rf directed energy.
This patent grant is currently assigned to Lockheed Martin Corporation. Invention is credited to Wayne K. Schroeder, Mark A. Turner, Brett A. Williams.
United States Patent |
7,820,990 |
Schroeder , et al. |
October 26, 2010 |
System, method and apparatus for RF directed energy
Abstract
Systems and methods are disclosed for emitting electromagnetic
(EM) energy. A source emits EM energy that is incident on a first
material. The first material transmits EM energy to a second
material. The second material can have a first surface adjacent to
the first material and a thickness and shape selected to stimulate
surface plasmon polaritons on the first surface of the second
material to resonate the EM energy transmitted from the first
material such that the resonated EM energy has an EM wavelength in
a narrow field of view with substantially no sidelobes.
Inventors: |
Schroeder; Wayne K. (Mansfield,
TX), Turner; Mark A. (Arlington, TX), Williams; Brett
A. (Iowa City, IA) |
Assignee: |
Lockheed Martin Corporation
(Bethesda, MD)
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Family
ID: |
39541506 |
Appl.
No.: |
12/000,298 |
Filed: |
December 11, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080149860 A1 |
Jun 26, 2008 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60873957 |
Dec 11, 2006 |
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Current U.S.
Class: |
250/493.1;
324/754.23; 324/754.24; 324/754.22 |
Current CPC
Class: |
G21K
1/06 (20130101); H05H 6/00 (20130101); G21K
1/08 (20130101); G21K 2201/067 (20130101) |
Current International
Class: |
G01R
31/26 (20060101) |
Field of
Search: |
;250/493.1,505.1
;324/765,750,753 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Barnes, William L., et al. "Surface Plasmon Subwavelength Optics."
Nature, vol. 42d, Aug. 14, 2003, pp. 824-830. cited by
other.
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Primary Examiner: Nguyen; Kiet T
Attorney, Agent or Firm: Buchanan Ingersoll & Rooney
PC
Parent Case Text
CROSS REFERENCE TO PRIOR APPLICATIONS
This application claims the benefit of priority of provisional
application No. 60/873,957 filed on Dec. 11, 2006, the entire
content of which is hereby incorporated by reference.
Claims
What we claim is:
1. A system for emitting electromagnetic (EM) energy comprising: a
source of EM energy; a first material that transmits incident EM
energy emitted from the EM source; and a second material having a
first surface adjacent to the first material and a thickness and
shape selected to stimulate surface plasmon polaritons on the first
surface of the second material adjacent the first material to
resonate the EM energy transmitted from the first material such
that the resonated EM energy has an EM wavelength in a narrow field
of view with substantially no sidelobes.
2. The system of claim 1, wherein the second material is different
from the first material.
3. The system of claim 1, wherein the first material is a
dielectric.
4. The system of claim 1, wherein the second material is a metal
having the first surface configured as a grating such that the
selected thickness and shape stimulate the surface plasmon
polaritons.
5. The system of claim 1, comprising a third material, wherein the
second material has a second surface adjacent to the third
material, and wherein the third material refracts the resonated EM
energy towards a target.
6. An apparatus for emitting electromagnetic (EM) energy
comprising: a first material having a first surface and a second
surface and configured to receive EM energy from an EM source; and
a second material having a first surface and a second surface and
configured relative to the first material to receive EM energy from
the first material, wherein the first surface of at least one of
the first and second materials includes an interface configured to
resonate the EM energy received via the first material and to
stimulate surface plasmon polaritons on at least one of the first
and second surfaces of the second material in response to the EM
energy, wherein the second material is configured to resonate the
EM energy at a wavelength in a narrow field of view with
substantially no sidelobes.
7. The apparatus of claim 6, wherein the second surface of the
second material is configured to emit light that is incident at a
predetermined angle.
8. The apparatus of claim 6, wherein at least one of the first and
second surfaces of the second material includes a grating.
9. The apparatus of claim 8, wherein the grating is applied in an
alternating pattern.
10. The apparatus of claim 6, wherein at least one of the first and
second surfaces of the first material includes a grating.
11. The apparatus of claim 6, wherein at least one of the first
surface and the second surface of the first material includes a
grating and at least one of the first and second surfaces of the
second material includes a grating.
12. The apparatus of claim 6, wherein the second material is of
varying thickness, and wherein at least part of the second material
has a wedge shape.
13. The apparatus of claim 12, wherein at least part of the second
material has a curve shape.
14. A method for illuminating a target comprising: supplying EM
energy from an EM source; and focusing the EM energy into a narrow
beam by using the EM energy to stimulate surface plasmon polaritons
on a metal layer located adjacent at least one dielectric
layer.
15. The method of claim 14, wherein the narrow beam has
substantially no sidelobes.
16. An apparatus for emitting electromagnetic (EM) energy
comprising: a first material having a first surface and a second
surface and configured to receive EM energy from an EM source; and
a second material having a first surface and a second surface and
configured relative to the first material to receive EM energy from
the first material, wherein the first surface of at least one of
the first and second materials includes an interface configured to
resonate the EM energy received via the first material and to
stimulate surface plasmon polaritons on at least one of the first
and second surfaces of the second material in response to the EM
energy, wherein at least one of the first and second surfaces of
the first material includes a grating.
17. The apparatus of claim 16, wherein at least one of the first
and second surfaces of the second material includes a grating.
Description
BACKGROUND
1. Field
Systems and methods are disclosed for emitting electromagnetic (EM)
energy.
2. Background Information
Surface plasmon polaritons are surface plasmons associated with
incident light waves that result when free space electromagnetic
waves couple to free electron oscillations (surface plasmons) in
metal. Surface plasmon polaritons are lightwaves trapped on a
conductive metal surface due to their interactions with electrons
on the conductive metal surface.
Metal supports collective surface oscillations of free electrons.
These collective surface oscillations can concentrate
electromagnetic fields on the nanoscale, enhancing local field
strength in a particular direction by several orders of magnitude.
Plasmon characteristics can be accessed at optical and radio
wavelengths. Normal propagating electromagnetic (EM) waves have
constant phase and amplitude in the same plane. Surface plasmons
and surface plasmon polaritons have planes of constant phase
perpendicular to those of constant amplitude, i.e. both are forms
of evanescent waves.
The primary responders to EM waves are electrons followed by polar
molecules. Even low inertia electrons can fail to keep up with high
frequencies depending on material used in constructing a detector.
The dependence on material is described by the index of refraction
(or dielectric constant or relative permittivity) and is a function
of EM frequency.
This dependence on index of refraction and on frequency (or
wavelength) is called a "dispersion relation". Surface plasmons on
a smooth planar metal display non-radiative electromagnetic modes;
i.e., the surface plasmons cannot decay spontaneously into photons
nor can light be coupled directly with surface plasmons.
The reason for this non-radiative nature of surface plasmons is
that interaction between light and surface plasmons cannot
simultaneously satisfy energy and momentum conservation; the
conservation of parallel momentum is not satisfied as represented
by the momentum wave-vector, k (where the magnitude of
k=2.pi./.lamda., with .lamda. being the EM wavelength). When
surface plasmons and light are made to be in resonance, the result
is a "surface plasmon polariton". The surface plasmon polariton is
an electromagnetic field in which both light and electron wave
distributions match in their momentum vector, i.e. they have the
same wavelength. This is also true for non-optical EM energy, e.g.,
radio waves.
Resonance and field enhancement can be made to take place if the
electromagnetic momentum wave vector is increased as in a
transparent medium with an index of refraction, n, to match
incident EM energy to the surface plasmon momentum Wave-vector, or
inversely, resonance can be achieved by roughening the metal
surface to impose a surface impedance (i.e. along the
dielectric/metal interface) in order to match free space
electromagnetic waves to surface plasmons. In practice, momentum
restrictions can be circumvented either by a prism coupling
technique to shorten electromagnetic wavelength or by a metal
surface grating, nano-structures such as holes, dimples, posts or
statically rough surfaces. This resonance results in the fields
associated with moving electron collections enhancing that of
electromagnetic waves at the matched wavelength.
There are a number of known ways in which to create surface plasmon
polaritons. For example, the Kretchmann-Rather attenuated total
reflection configuration includes a dielectric prism mated with a
thin metal film. For the Kretchmann-Rather configuration, a plasmon
does not ride on the dielectric/metal interface. Plasmons arise
instead on the back, metal/air interface. Once EM waves incident on
the dielectric/metal interface exceed the so-called critical angle
of total internal reflection they establish evanescent waves, which
penetrate the metal film to some skin depth. Such light induced
evanescent waves excite surface plasmon polaritons on the side of
the metal opposite the dielectric.
SUMMARY
Disclosed is an exemplary system for emitting electromagnetic (EM)
energy, comprising a source of EM energy, a first material that
transmits incident EM energy emitted from the source; and a second
material. The second material has a first surface adjacent to the
first material and a thickness and shape selected to stimulate
surface plasmon polaritons on the first surface of the second
material adjacent the first material to resonate the EM energy
transmitted from the first material such that the resonated EM
energy has an EM wavelength in a narrow field of view with
substantially no sidelobes.
Also disclosed is an apparatus for emitting electromagnetic (EM)
energy, comprising a first material that receives EM energy from an
EM source, and a second material that receives the EM energy from
the first material. A first surface of the second material includes
an interface configured to resonate the EM energy received via the
first material and to stimulate surface plasmon polaritons on a
second surface of the second material in response to the EM
energy.
Also disclosed is an exemplary method for illuminating a target,
comprising supplying EM energy from an EM source. The EM energy is
focused into a narrow beam by using EM energy to stimulate surface
plasmon polaritons on a metal layer located adjacent at least one
dielectric layer.
DESCRIPTION OF THE DRAWINGS
Exemplary embodiments will be described in relation to the
following figures wherein:
FIG. 1 illustrates an exemplary embodiment of an apparatus for
emitting electromagnetic (EM) energy;
FIGS. 2A-2C illustrate EM energy coupling between material layers
in accordance with an exemplary apparatus for emitting
electromagnetic energy;
FIGS. 3A-3E illustrate exemplary surface features of dielectric and
metallic layers;
FIGS. 4A-4C illustrate exemplary metal layers for beamwidth tuning;
and
FIG. 5 illustrates an exemplary system 400 for emitting
electromagnetic (EM) energy in a narrow field of view without side
lobes.
DETAILED DESCRIPTION
FIG. 1 illustrates an exemplary apparatus 100, such as an antenna,
for emitting electromagnetic (EM) energy. The apparatus comprises a
source of EM energy 102. A first material, such as an input
dielectric layer 106, is provided to transmit incident EM energy
emitted from the EM source. The first material is thus configured
(e.g., shaped, sized and positioned relative to the EM source and
to other components of the apparatus 100) to receive EM energy from
the EM source. The input dielectric layer 106 can be a collimator
such as a Duroid, on other material having similar
characteristics.
A second material, such as a metal layer 104, has a first surface
adjacent a second material having a first surface adjacent to the
first material and a thickness and shape selected to stimulate
surface plasmon polaritons on the first surface of the second
material adjacent the first material to resonate the EM energy
transmitted from the first material such that the resonated EM
energy has an EM wavelength in a narrow field of view with
substantially no sidelobes. The second material is thus configured
(i.e., shaped of an appropriately selected material, sized and
positioned) relative to the first material to receive EM energy
from the first material. With this configuration, the first surface
of the second material includes an interface configured to resonate
the EM energy received via the first material and to stimulate the
surface plasmon polaritons on a second surface of the second
material in response to the EM energy.
While the first sidelobes of traditional, non-tailored, uniformly
illuminated circular apertures are 17 dB below their main beam
peak, exemplary embodiments described herein can include plasmonic
enhanced apertures that provide an additional 13 dB or greater,
i.e. -30 dB first sidelobes under the same conditions.
A third layer, such as an output dielectric layer 108, can also be
provided. The output dielectric layer 108 can be a collimator, such
as a Duroid, prism, air, vacuum, or other material having similar
characteristics, that is configured to refract EM energy
transmitted from the metal layer 104 towards a target.
The metal layer 104 can be a metal such as silver, gold, or
aluminum or an alloy. Besides metals like silver, gold or aluminum,
polaritons as employed by this application may also propagate in
semiconductor materials and doped semiconductor materials as long
as their charge density results in a plasma frequency at least sqrt
(2) times that of the incident frequency of interest, thus
resulting in a permittivity real part less than negative one.
Intrinsic semiconductors, such as Germanium, provide change
densities high enough that a negative index can be satisfied below
10 GHz radio frequencies, while doped materials like 4H--SiC doped
with 2.times.10.sup.17 cm.sup.-3 nitrogen donor atoms at 300K more
than satisfy a negative index well above 10 GHz radio frequencies.
In an exemplary optical domain, the thickness of the metal layer
104 can be within the range of approximately 20 nanometers to 80
nanometers or more or less as desired for a given application. In
radio frequency applications, the metal film thickness can be 0.001
to 0.00004 inches, or more or less as desired for a given
application. For example, in an application employing X-band
frequency (e.g., 8-12 GHz), the thickness of the metal film can,
for example, be within the range of 0.00004 inches.
The input dielectric layer 106 is adjacent to a first surface 104a
of the metal layer 104 (e.g., in direct contact, or in sufficiently
close proximity as to function in accordance with the objectives
described herein). The output dielectric layer 108 is adjacent to a
second surface 104b of the metal layer 104. Both the input and
output dielectric layers 106, 108 can be implemented as a Duroid or
similar medium having indices of refraction of approximately 1.5 or
lesser or greater based on the desired output. The input and output
dielectric layers 106, 108 can have thicknesses of approximately
0.100 inches or lesser or greater.
The lengths of the input and output dielectric layers 106, 108 and
metal layer 104 can be approximately 1.25 inches in length, (or
more or less) as desired for a given application and the EM energy
to be transmitted therethrough and emitted as an EM wavelength. In
a relatively narrow field of view (i.e., narrow relative to the
field of view of the EM energy supplied from the EM source).
The metal layer 104 has a first surface 104a that is adjacent to
the input dielectric layer 106, and a second surface 104b that is
adjacent to the output dielectric layer 108. The metal layer 104
has a thickness selected to stimulate surface plasmon polaritons on
the second surface 104b of the metal layer 104 for EM energy having
a given EM wavelength incident on the input dielectric layer 106
beyond a critical angle (e.g., an angle of EM incidence at which
surface plasmon polaritons are generated after attenuated total
internal reflection from the dielectric interface creates
evanescent waves in the metal). Different metals, for example, gold
and silver, can be used to provide different contributions to
accuracy. Gold and silver, for example, can offer a desired field
of view of, for example, .+-.10.degree..
As the incident angle of the received electromagnetic energy on the
outer surface of the input dielectric layer 106 increases, the
amount of energy transmitted into the dielectric medium decreases
and energy from the surface plasmon polaritons also decreases. When
the incident angle on the outer surface (interface) of the first
dielectric layer 106 (e.g. air/dielectric) increases or extends
past 90.degree., little or no further transmission into the
dielectric occurs.
To facilitate collecting EM energy, the second surface 104b of the
metal layer 104 can be roughened in comparison to the first surface
104a of the metal film. The roughness of the second surface 104b of
the metal layer 104 can be selected to produce a desired amplitude
of the EM energy generated at the second surface 104b by the
stimulated surface plasmon polaritons. This roughness can be within
the range of approximately 1/500.sup.th or 1/1000.sup.th (or lesser
or greater as desired for a given application) of the EM wavelength
received at the surface of the input dielectric layer 106. The
surface plasmon polaritons can serve as an intermediary of incident
EM energy, i.e. surface plasmon polaritons escort energy through
the metal film over a narrow range of incident angles upon the
dielectric/metal interface while rejecting those incident angles
outside the range of angles.
The thickness of the metal film can be less than a skin depth of a
photonic evanescent wave penetrating the metal from the maximum
skin depth of the photonic evanescent wave at the first interface
of the dielectric layer 104 and the metal layer 104. This roughness
on the second surface 104b of the metal layer 104 can be created by
etching, lithography, grating, "sand blasting" utilizing small
plastic pellets as the "sand", or other suitable methods for
providing a desired roughness. The roughness can be used to
generate and enhance the EM energy output by the surface plasmon
polaritons. The first surface 104a of the metal layer 104 can be
warped to provide a selected and fixed field of view, such that the
resulting EM energy is focused in a narrow beam that has
substantially no side lobes.
The roughness can include various characteristics that influence
the EM energy output by the surface plasmon polaritons. For
example, a frequency bandwidth of the output EM energy can depend
on grating shape. A 10% bandwidth (.+-.5% about center frequency)
can be produced by square semiconductor gratings. Grating shape
influences bandwidth by limiting momentum wave vector match
(k-match) options presented to incident electromagnetic energy in
much the same way as the Fourier Transform of a square pulse in the
time domain produces many frequency components in the frequency
domain. Each specific frequency from such a transform is a sine
wave that is required when recombining all such components in order
to reconstitute the square pulse. The Fourier Transform of a sine
wave is, however, a sine wave. Likewise, a sine wave grating can
limit a frequency over which incident EM energy can k-match to
surface plasmons in order to create surface plasmon polaritons,
thereby limiting bandwidth.
FIGS. 2A-2C illustrate EM energy coupling between either of the
input and output dielectric layers 106, 108 and the metal layer
104. An output coupling of EM energy occurs when at least one
momentum wave vector k.sub.m (impulse) of the EM energy traveling
through the metal layer 104 matches at least one momentum wave
vector k.sub.od of the EM energy of the output dielectric 108.
Similarly, an input coupling of EM energy occurs when at least one
momentum wave vector k.sub.id (impulse) of the EM energy traveling
through the input dielectric layer 106 match at least one momentum
wave vector k.sub.m of the EM energy of the metal layer 104.
As shown in FIG. 2A, the coupling of EM traveling between the metal
layer 104 and the output dielectric layer 108 can be impacted by
the refraction index of the output dielectric layer 108. For
example, if the output dielectric layer 108 comprises a material
having a low refractive index, e.g. air, the EM energy traveling
between the metal layer 104 and the output dielectric layer 108
will not be matched. On the other hand, if the output dielectric
layer 108 comprises a material having a high refractive index, e.g.
a prism, the EM energy traveling between the metal layer 104 and
the output dielectric layer 108 will couple (resonate), and thus
passage of EM energy from the second surface 104b of the metal
layer 104 to the output dielectric layer 108 can occur.
As shown in FIG. 2B, the coupling of EM energy traveling between
the metal layer 104 and the output dielectric 108 can be impacted
by the angle of incidence of the EM energy. For example, if the EM
energy is incident on the second surface 104b of the metal layer
104 at an angle below .theta..sub.i, then the EM energy will not
enter the output dielectric layer 108 since the momentum wave
vector k.sub.m of the metal layer 104 is larger than the momentum
vector k.sub.od of the output dielectric layer 108. If the EM
energy is incident on the second surface 104b of the metal layer
104 at an angle greater than .theta..sub.i, then the momentum
vector k.sub.od of the output dielectric 108 will be increased such
that it matches the momentum vector k.sub.m of the metal layer 104.
One of ordinary skill will recognize that the .theta..sub.i can be
determined by the surface features of at least one of the metal
layer 104 and the output dielectric layer 108.
FIG. 2C illustrates an input coupling of EM energy traveling
between the input dielectric layer 106 and the metal layer 104. As
shown, without the roughness (i.e. grating) being established on
the first surface 104a of the metal layer 104 the momentum vectors
k of the polaritons are longer and thus not matched to the momentum
vectors of the EM energy traveling through the input dielectric
layer 106. On the other hand, if the grating is established on the
first surface 104a such that periodic surface features of the
grating are sufficient to shorten the momentum vector of the
polaritons, then the EM energy will traverse the first surface 104a
into the metal layer 106. For example, for a sine-wave a momentum
wave vector for a grating having a grating period .alpha. can be
represented as k.sub.g=2.pi./.alpha.. There are a small set of
momentum wave vectors (k) that enable the EM energy to pass between
the various material layers. As such if the momentum vectors
between the layers do not overlap (i.e., the EM energy fails to
resonate) then the material layers will operate as a mirror.
Surface features, such as gratings, can be applied to any one or
combination of the material layers (i.e., metal layer 104, input
dielectric layer 106, and/or output dielectric layer 108) as
desired. For example, a grating can be applied to any one or all
surfaces of a material layer, such that a grating appears on a
single surface of a selected material layer, both surfaces of a
selected material layer, alternating surfaces of a combination of
material layers, or any other application scheme as desired. While
polaritons are bound only to metallic surfaces, surface features on
a dielectric can mate to the metallic surface to enhance or adjust
antenna beam characteristics such as main lobe width and sidelobe
level. Thus for specific dielectric surface features, momentum wave
vector matching (k-matching) options other than those of a
dielectric constant or incident angle can be achieved as discussed
above in FIGS. 2A and 2B.
FIGS. 3A through 3C illustrate interface options between the metal
layer 104 and the input and/or output dielectric layers 106, 108.
In the example of FIG. 3A, a flat Duroid dielectric layer 106 is
coupled to an indium antimonide (InSb) semiconductor layer 104. The
semiconductor layer 104 has a grating applied to a surface that
interfaces with the dielectric layer 106. As shown in FIG. 3B, a
flat Duroid dielectric layer 106 is coupled to an indium antimonide
(InSb) semiconductor layer 104 having a grating 110 applied to both
surfaces. FIG. 3C illustrates a first flat Duroid dielectric layer
106 that is coupled to a surface of an indium antimonide (InSb)
semiconductor layer 104. A second flat Duroid dielectric layer 108
is coupled to a surface of the semiconductor layer 104 that is
opposite the first dielectric layer 106. In this example, the
semiconductor layer 104 has a grating 110 applied to each surface
that interfaces the first and second dielectric layers 106, 108. As
shown in FIG. 3D, a flat Duroid dielectric layer 106 is coupled to
an indium antimonide (InSb) semiconductor layer 104. The
semiconductor layer 104 has a grating 110 applied to both surfaces
in an alternating pattern. In the example of FIG. 3E, a flat Duroid
dielectric layer 106 is coupled to an indium antimonide (InSb)
semiconductor layer 104 having a grating applied to an interface
between the layers. The gaps resulting at the interface are filled
with air.
Sidelobe suppression is enhanced by a variety of factors. For
example, in the case of gratings as the surface feature on any of
the metal layer 104, the input dielectric layer 106, and the output
dielectric layer 108, the greater the number of gratings over a
finite antenna length, the greater is sidelobe suppression. The
enhanced sidelobe suppression characteristic makes larger
apertures, which allows more gratings, of particular value for beam
transmission. The grating height between channels and peaks can
also reduce sidelobe levels to a level that is also determined by
wavelength of operation and material characteristics such as
relevant material permittivity. As a result, an available device
depth can be a design parameter that influences the amount of
sidelobe suppression and/or beam steering. Feature "fill", e.g.
grating fill (width of peaks) and period contribute to peak
incident angle reception and thus main beam direction.
FIGS. 4A-4C illustrate exemplary metal layers 106 for beamwidth
tuning. As shown in FIG. 4A, the metal layer 104 can have a
substantially rectangular shape of a substantially uniform
thickness. In this configuration, the metal layer 104 transmits
nearly all EM energy incident of the first face 106a. The EM energy
incident on the first face 106a satisfies a total internal
reflection (TIR) requirement for resonance of the metal layer 104
so that two beams of limited beamwidth are produced.
As shown in FIG. 4B, the metal layer 104 can have a substantially
wedge shape of varying thickness along the length of the first and
second surfaces 106a, 106b. In this configuration, the metal layer
104 rejects EM energy that is not incident upon the first surface
104a at a predetermined angle. The EM energy that is incident on
the first surface 104a at the predetermined angle resonates within
a resonance region. The angle of the first surface 104a determines
the location of the resonance region within the metal layer 104
such that any EM energy that is not incident upon the first surface
106 within an appropriate range of angles will be rejected (i.e.,
will not resonate). The EM energy exiting the metal layer 104 at
the second surface 104b can have, for example, a 20.degree.
beamwidth for a resonance region at a width of 2.5.degree.. In this
configuration, the beamwidth cutoff angle can be controlled by the
width of the resonance region (i.e., resonance width). Resonance
width is a range of incident angles over which incident EM energy
can resonate with (i.e. couple to) plasmons on a surface of the
metal layer 104. Resonance width can be determined by beamwidth
tuning as well as material choice.
As shown in FIG. 4C, the metal layer 104 can have a combined
wedge/curve shape of varying thickness along the length of the
first and second surfaces 106a, 106b respectively. The wedge/curve
configuration can result in the rejection of EM energy that is not
incident upon the first surface 104a at a predetermined angle,
because the EM energy will not resonate in the resonance region.
The EM energy exiting the metal layer at the second surface 104b
can have, for example, a 30.degree. beamwidth at a resonance width
of 2.5.degree.. The beamwidth cutoff angle can be controlled, for
example, by various parameters such as the shape and
characteristics of the material layers and a length of the
antenna.
One of ordinary skill can appreciate the constraints on an antenna
that can be realized based on the characteristics of the metal
layer 104. For example, the material composition of the metal layer
104 can determine incident angle of the first surface 104a for
achieving resonance. The angle of the first surface 104a can
determine the cutoff angle of the EM energy and/or the location of
the resonance area depending on the configuration. The curvature of
the first surface 104a can also control the location of the
resonance area.
To facilitate the transmission of EM energy at specific narrow
angles in accordance with exemplary embodiments disclosed herein,
the input and output dielectric layers 104, 108 and the metal layer
104 can encompass various characteristics.
For example, the metal layer 104 can be doped to a charge density
so that an appropriate negative permittivity for a chosen transmit
frequency is attained. The roughness of the first surface 104a of
the metal layer 104, such as a grating, can be shaped (e.g.,
square, round) so that the EM energy can resonate at the second
surface 104b at a predetermined frequency bandwidth. The momentum
wave vector k.sub.od of the output dielectric 108 can be matched to
the momentum wave vector k.sub.m2 at the second surface 104b of the
metal layer 104 based on a desired output angle of the EM energy to
be transmitted. The momentum wave vector k.sub.id of the input
dielectric 106 can be matched to the momentum wave vector k.sub.m1
at the first surface 104a of the metal layer 104 based on the
refractive index of the input dielectric 106 and the angle of
incidence of the EM energy. The refractive index of the input
dielectric 106 can be smaller than the refractive index of the
output dielectric.
The outer surfaces of the input and output dielectrics 104, 108 can
be configured (i.e. shaped) so that the EM energy has an
appropriate angle of incidence at each of the respective outer
surfaces of the input and output dielectric 104, 108.
FIG. 5 illustrates an exemplary system 400 for transmitting
electromagnetic (EM) energy in a narrow beam (i.e., narrow relative
to the EM energy supplied by a source), without side lobes. The
system 400 includes a source 402 that supplies EM energy and an
antenna 404 that directs the emitted EM energy to illuminate a
target through a narrow beam having no side lobes. The antenna is
configured as described in FIG. 1 such that a metal layer 104 is
disposed between an input dielectric layer 106 and an output
dielectric layer 108. The metal layer 104 includes a first surface
104a that is adjacent to an inner surface of the input dielectric
layer 106 and a second surface 104b that is adjacent to an inner
surface of the output dielectric layer 108. In this example, the
metal layer 104 is configured to k-match Ka-band radio frequency
energy with linear, rectangular gratings on an intrinsic
(non-doped) indium antimonide semiconductor layer with
period=3.5828 mm, fill=1.5772 mm, semiconductor thickness at
grating channels=0.2250 mm, semiconductor thickness at grating
peaks=0.2250 mm, a layer of Arlon CuClad (for thermal matching) of
thickness 0.0381 mm over semiconductor peaks, and thickness 0.2631
mm over semiconductor channels, overlaid with flat Duroid of
refraction index=1.53, and thickness 3.175 mm.
As shown in FIG. 5, the source 402 supplies EM energy on a surface
of the antenna 404 at a predetermined angle. At the antenna, the
material layers (104, 106, 108) are configured such that, as the EM
energy travels between the material layers, at least a portion EM
energy is coupled and emitted in a narrow beam devoid of side lobes
towards a target. The interaction of the material layers based on
any combination of the respective thickness, shape, and/or material
composition of each layer determines the surface plasmon polaritons
located on a surface of the metal layer that are to be stimulated
to emit the EM beam.
Exemplary methods for illuminating a target with EM energy are also
encompassed by the present discloser. Such an exemplary method
includes supplying EM energy from an EM source; and focusing the EM
energy into a narrow beam by using the EM energy to stimulate
surface plasmon polariton on a metal layer located adjacent at
least one dielectric layer.
One of ordinary skill can appreciate that the exemplary embodiments
described herein enable the EM energy to be transmitted in various
adverse environmental conditions such as rain, clouds, dust, fog,
snow, or any other condition that can be considered unfavorable for
energy transmission.
Moreover, it is understood that the exemplary embodiments can be
implemented in various applications such as the transmission of
communication signals and data (e.g., cellular or wireless
communication), and energy transmission through solar panels.
It will be appreciated by those skilled in the art that the present
invention can be embodied in other specific forms without departing
from the spirit or essential characteristics thereof. The presently
disclosed embodiments are therefore considered in all respects to
be illustrative and not restricted. The scope of the invention is
indicated by the appended claims rather than the foregoing
description and all changes that come within the meaning and range
and equivalence thereof are intended to be embraced therein.
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